The animal viruses provide technically convenient lipid membrane systems with medically interesting surface glycoprotein activities for the study of basic protein-lipid and protein-carbohydrate interactions. This proposal outlines the three dimensional X-ray crystallographic structure determination of the major surface antigen, the haemagglutinin glycoprotein, of influenza virus, along with electron microscopic and biochemical characterizations of its hydrophobic "tail" peptide. The haemagglutinin is the most suitable glycoprotein for the structural studies proposed, and offers the opportunity for understanding its functions in viral maturation by budding, and host cell binding and membrane penetration at infection. Furthermore, biannual influenza epidemics and occasional pandemics result from the haemagglutinin's ability to undergo marked antigenic variations (drifts and shifts) while preserving its biological activity. Knowledge of the three-dimensional structure of the haemagglutinin should reveal the basis for this evolutionarily and medically significant process. This proposal also outlines preliminary biochemical and structural characterization of the Sendai virus fusion protein active in cell membrane fusion events and viral penetration; and of a protein underlying viral membranes.